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2022-08-11
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Holographic anti-counterfeiting original production and process analysis (middle)

recording method of rainbow holographic original from the above analysis, we know that when the rainbow hologram is illuminated with white light, different colors can be observed at the angle corresponding to the reconstruction slit image of different wavelengths, which indicates that if the slit position is properly designed during the recording of rainbow holography, a specific monochromatic or color image can be observed at a specific angle. In order to make the rainbow hologram reconstructed by white light can reproduce the color image at a certain viewing angle, the position of the slit has been specially designed. This book introduces the method of false color coding design using the three slit area segmentation method. The so-called false color means that the color of the reconstructed image is inconsistent with the color of the object, while the true color means that the color of the reconstructed image is the same as the punch code object

1. False color coding monochrome design

to get the pre-3. Transmission speed: set the color combination, you must set the seam spacing according to the optical path parameters. This section mainly discusses how to design the colors of different parts of each layer or one layer of the original holographic image, specifically, how to design the distance between the slots according to the angle between the reference light path, the object light wave and the recording wavelength

due to the limitation of the recording material used to make embossed rainbow holograms, purple laser is used during recording, so generally speaking, the slit is often expected to be designed on both sides of the central normal of the dry plate in the arrangement of light path, so the slit position is often taken in the design. Multicolor products with low color requirements are all from production and processing to the formation of plastic product information map. According to the parameters of and, the distance between each slit as long as the color of the reproduction image is separated. When the slit width is small or large, the color of the reconstructed image is relatively pure. Limited by the resolution of recording holographic materials, it is generally about 35 °. When the slit width is small, the object light for making holograms is relatively weak. Note that in fact, when reconstructing a hologram with white light, the slits of each wavelength are not at the same depth

2 pseudo color coded multicolor design

3 multi slit rainbow holography

in the recording optical path of two-step rainbow holography, we see that only a narrow part of the main hologram is used. It is easy to imagine that a dry plate is divided into several zonal areas, and each zonal area records an object or different parts of an object. When recording in the second step, make them reproduce and record on a hologram h at the same time, which is called multi slit rainbow holography. When the hologram is reproduced with laser illumination, observe the position of a slit image, and you can see the image of the corresponding object. If white light is used for reproduction, it will be seen that the recorded objects appear in different colors; If different parts of an object are recorded, the whole object can be seen in different colors at a certain position, which is called false color coding of the object. Multi slit rainbow holography can also be completed in one step, which mainly sets multiple slits on the entrance or exit pupil of the imaging lens

the original recording method of encrypted rainbow hologram is mainly to generate the color sequence of the object through the transverse area segmentation of the main hologram and the design of the dispersion observation window, so as to achieve the purpose of encryption and anti-counterfeiting. The encryption methods it adopts mainly include moire technology encryption method and optical anti-counterfeiting method of position phase coding, which can also meet the unique needs of different brand companies (OEMs) other than international standards

moire encryption method

encrypted holographic identification refers to placing a password on a part or the whole page of the original holographic identification image. The password takes the transformation spectrum or optical phenomenon of some special functions as the physical model. When the password finally appears in the form of optical pattern, the encryption method is called "explicit encryption". The "implicit encryption method" must use a decoder to read the designed password. The difference between implicit password and explicit password is that implicit password is hidden, and the observer will not find anything special about the holographic logo with implicit password. However, as long as you have the physical model of another function used in the recording process, that is, the decoder, paste it on the label and rotate it by an angle, you can read the result of the superposition of the two function equations designed in advance, that is, a new image. And the new image and the image of the two functions that generate it can be completely different. Because of this, "implicit cryptography" is more effective than many current anti-counterfeiting methods in distinguishing authenticity and anti-counterfeiting

1. The basic law of moire phenomenon

optical moire images are formed by the superposition of two periodic patterns with similar frequencies. We use the superposition of two gratings to illustrate the formation of MOA fringes, and the characteristics of the grating are characterized by its transmission coefficient or transmission coefficient

(to be continued)

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